Resist composition and patterning process

ABSTRACT

An additive polymer comprising recurring units derived from a fluorosulfonamide-substituted styrene and recurring units derived from a stilbene, styrylnaphthalene, dinaphthylethylene, acenaphthylene, indene, benzofuran, or benzothiophene derivative is added to a polymer capable of increasing alkali solubility under the action of acid to formulate a resist composition. The resist composition can minimize outgassing from a resist film during the EUV lithography and form a resist film having a hydrophilic surface sufficient to prevent formation of blob defects on the film after development.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2012-277747 filed in Japan on Dec. 20, 2012,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition, and more particularly toa chemically amplified positive resist composition comprising a polymercomprising recurring units having an acid labile group in blend with apolymeric additive comprising recurring units derived from afluorosulfonamide-substituted styrene and recurring units derived from amonomer selected from stilbene, styrylnaphthalene, dinaphthylethylene,acenaphthylene, indene, benzofuran, and benzothiophene derivatives; anda patterning process using the same.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, extreme ultraviolet (EUV)lithography of 13.5 nm wavelength, and double patterning version of theArF lithography, on which active research efforts have been made.

With respect to high-energy radiation of very short wavelength such aselectron beam (EB) or x-ray, hydrocarbons and similar light elementsused in resist materials have little absorption. Then polyhydroxystyrenebase resist materials are under consideration. Resist materials for EBlithography are practically used in the mask image writing application.Recently, the mask manufacturing technology becomes of greater interest.Reduction projection exposure systems or steppers have been used sincethe time when the exposure light was g-line. While their demagnificationfactor was ⅕, a factor of ¼ is now used as a result of chip sizeenlargement and projection lens diameter increase. It becomes of concernthat a dimensional error of a mask has an impact on the dimensionalvariation of a pattern on wafer. It is pointed out that as the patternfeature is reduced, the value of a dimensional variation on the waferbecomes greater than the value of a dimensional error of the mask. Thisis evaluated by a mask error enhancement factor (MEEF) which is adimensional variation on wafer divided by a dimensional error of mask.Patterns on the order of 45 nm often show an MEEF in excess of 4. In asituation including a demagnification factor of ¼ and a MEEF of 4, themask manufacture needs an accuracy substantially equivalent to that forequi-magnification masks.

The exposure system for mask manufacturing made a transition from thelaser beam exposure system to the EB exposure system to increase theaccuracy of line width. Since a further size reduction becomes possibleby increasing the accelerating voltage of the electron gun in the EBexposure system, the accelerating voltage increased from 10 keV to 30keV and reached 50 keV in the current mainstream system, with a voltageof 100 keV being under investigation.

As the accelerating voltage increases, a lowering of sensitivity ofresist film becomes of concern. As the accelerating voltage increases,the influence of forward scattering in a resist film becomes so reducedthat the contrast of electron image writing energy is improved toameliorate resolution and dimensional control whereas electrons can passstraightforward through the resist film so that the resist film becomesless sensitive. Since the mask exposure tool is designed for exposure bydirect continuous writing, a lowering of sensitivity of resist filmleads to an undesirably reduced throughput. Due to a need for highersensitivity, chemically amplified resist compositions are contemplated.

Thinning of resist film is in progress to facilitate reduction ofpattern feature in the EB lithography for mask manufacturing and toprevent the pattern from collapsing due to a higher aspect ratio duringdevelopment. In the case of photolithography, a thinning of resist filmgreatly contributes to resolution improvement. This is becauseintroduction of chemical mechanical polishing (CMP) or the like hasdriven forward device planarization. In the case of mask manufacture,substrates are flat, and the thickness of processable substrates (e.g.,Cr, MoSi or SiO₂) is predetermined by a percent light shield or phaseshift control. The dry etch resistance of resist film must be improvedbefore the film can be reduced in thickness.

It is generally believed that there is a correlation between the carbondensity and the dry etch resistance of resist film. For EB writing whichis not affected by absorption, resist materials based on novolac resinshaving better etch resistance have been developed. Indene copolymersdescribed in Patent Document 1 and acenaphthylene copolymers describedin Patent Document 2 are expected to have improved etch resistance dueto a high carbon density and a robust main chain structure based oncycloolefin structure.

Also, with respect to the soft x-ray (EUV) lithography at wavelength5-20 nm, the reduced absorption of carbon atoms was reported. Increasingthe carbon density is effective not only for improving dry etchresistance, but also for increasing the transmittance in the soft x-raywavelength region.

A tradeoff among sensitivity, edge roughness and resolution is reported.Increasing sensitivity leads to reductions of edge roughness andresolution. Controlling acid diffusion improves resolution at thesacrifice of edge roughness and sensitivity. Addition of an acidgenerator capable of generating a bulky acid is effective forsuppressing acid diffusion, but leads to reductions of edge roughnessand sensitivity as pointed out above. It is then proposed tocopolymerize a polymer with an acid generator in the form of an oniumsalt having polymerizable olefin. Patent Documents 3 to 5 disclosesulfonium salts having polymerizable olefin capable of generating asulfonic acid and similar iodonium salts. A photoresist using a basepolymer having a polymerizable acid generator copolymerized thereinexhibits reduced edge roughness due to controlled acid diffusion anduniform dispersion of acid generator within the polymer, succeeding inimproving both resolution and edge roughness at the same time.

One problem in the EUV lithography is that outgassing components from aresist film during exposure adsorb to the surface of a reflecting mirrorand mask in the exposure tool to reduce their reflectivity. It isproposed to form a protective film atop the resist film for the purposeof reducing the outgassing. Then, a coater cup is necessary for coatingof the protective film. At the early stage of the immersion lithography,a protective film was applied in order to prevent the acid generatorfrom being leached out of the resist film into water. However, theprovision of a protective film brings about a drop of throughput and arise of material cost. Because of these problems, the protective film isgradually going out of use. Under the circumstances, it would bedesirable to have a resist material for the EUV lithography which caneliminate or reduce outgassing without the aid of protective film.

Patent Documents 6 and 7 disclose resist materials wherein a copolymerof a styrene derivative and a fluorinated recurring unit containingfluorosulfonamide or a copolymer of vinylnaphthalene and a fluorinatedrecurring unit containing fluorosulfonamide is added to a base polymer.When these resist materials are spin coated, the polymer having styreneunits or vinylnaphthalene units segregates in a surface layer of thecoating, achieving both water-repellent and anti-reflection effects.Patent Documents 6 and 7 also refer to the suppression of outgassing inthe EUV lithography.

However, the styrene and vinylnaphthalene units achieve insufficientsuppression of outgassing. There exists a desire to have a resistsurface modifying material capable of effectively shutting offoutgassing.

Patent Document 8 discloses that a polymer comprisingfluorosulfonamide-substituted styrene units is added to a resistmaterial for ArF immersion lithography. It does not describe whether ornot the addition of a polymer comprising fluorosulfonamide-substitutedstyrene units is effective for reducing the outgassing during EUVlithography process. In fact, the addition of a polymer comprisingfluorosulfonamide-substituted styrene units is not effective for fullysuppressing the outgassing during EUV lithography process.

CITATION LIST

Patent Document 1: JP 3865048

Patent Document 2: JP-A 2006-169302

Patent Document 3: JP-A H04-230645

Patent Document 4: JP-A 2005-084365

Patent Document 5: JP-A 2006-045311

Patent Document 6: JP 4771974

Patent Document 7: JP 4900603

Patent Document 8: JP-A 2012-073508 (WO 2012/043866)

DISCLOSURE OF INVENTION

An object of the present invention is to provide a resist compositionwhich can minimize outgassing from a resist film during the EUVlithography and form a resist film having a hydrophilic surfacesufficient to prevent formation of blob defects on the film afterdevelopment; and a pattern forming process using the same.

The inventors have found that a satisfactory resist composition isobtainable by adding a polymeric additive comprising recurring unitsderived from a fluorosulfonamide-substituted styrene and recurring unitsderived from at least one monomer selected from stilbene,styrylnaphthalene, dinaphthylethylene, acenaphthylene, indene,benzofuran, and benzothiophene derivatives to a polymer capable ofincreasing alkali solubility under the action of acid.

According to the invention, a fluorochemical surfactant of polymer typecomprising recurring units derived from a fluorosulfonamide-substitutedstyrene and recurring units derived from at least one monomer selectedfrom stilbene, styrylnaphthalene, dinaphthylethylene, acenaphthylene,indene, benzofuran, and benzothiophene derivatives is added to a polymeror base resin to formulate a resist material. When the resist materialis coated, a layer of the polymer comprising recurring units derivedfrom a fluorosulfonamide-substituted styrene and recurring units derivedfrom at least one monomer selected from stilbene, styrylnaphthalene,dinaphthylethylene, acenaphthylene, indene, benzofuran, andbenzothiophene derivatives is formed on the surface of the resist film.This surface layer has a high film density enough to prevent outgassingcomponents from escaping from within the resist film. In addition, sincethe fluorochemical surfactant of polymer type comprising recurring unitsderived from a fluorosulfonamide-substituted styrene and recurring unitsderived from at least one monomer selected from stilbene,styrylnaphthalene, dinaphthylethylene, acenaphthylene, indene,benzofuran, and benzothiophene derivatives dissolves in an alkalinedeveloper, it renders the resist surface after exposure and developmentmore hydrophilic and is thus effective for suppressing formation of bloband bridge defects. By virtue of these advantages, the resist materialis best suited as a mask blank resist material having long-termstability after coating and stability against exposure in vacuum and anEUV resist material featuring minimal outgassing in vacuum. A patternforming process using the resist material is also provided.

In one aspect, the invention provides a resist composition comprising apolymer capable of increasing alkali solubility under the action of acidas base resin, and a polymer having the general formula (1) as polymericadditive.

Herein R¹ is a single bond or a straight or branched C₁-C₄ alkylene, R²is fluorine, or a straight, branched or cyclic C₁-C₆ alkyl, phenyl oralkyl-substituted phenyl group which contains at least one fluorineatom, R³ and R⁴ are each independently selected from the groupconsisting of hydrogen, hydroxyl, straight, branched or cyclic C₁-C₁₀alkyl, alkoxy, acyloxy, C₂-C₆ alkenyl, C₆-C₁₀ aryl, cyano, nitro, aminoand halogen, X¹ and X² each are phenylene or naphthylene, m is 1 or 2,R⁵ and R⁶ are each independently selected from the group consisting ofhydrogen, halogen, straight or branched C₁-C₄ alkyl, alkoxy, acyloxy,hydroxyl, carboxyl, and alkoxycarbonyl, M is methylene, oxygen atom orsulfur atom, p, q−1, q−2 and q−3 are numbers in the range: 0<p<1.0,(q−1)<1.0, 0 (q−2)<1.0, 0 (q−3)<1.0, and 0<(q−1)+(q−2)+(q−3)<1.0.

Typically the resist composition is a chemically amplified positiveresist composition.

In a preferred embodiment, the polymer as base resin comprises recurringunits having an acid labile group and recurring units having a hydroxyland/or lactone ring adhesive group.

In a more preferred embodiment, the polymer as base resin has a weightaverage molecular weight of 1,000 to 500,000, and the recurring unitshaving an acid labile group are recurring units of at least one typeselected from recurring units (a1) and (a2) having a carboxyl and/orphenolic hydroxyl group substituted with an acid labile group, asrepresented by the general formula (2).

Herein R¹⁰ and R¹² are each independently hydrogen or methyl, R¹¹ andR¹³ each are an acid labile group, Y¹ is a single bond, a C₁-C₁₂ linkinggroup having at least one of ester (—COO—), lactone ring, phenylene andnaphthylene, a phenylene group or a naphthylene group, Y² is a singlebond, ester (—COO—) group or amide (—CONH—) group, a1 and a2 are numbersin the range: 0≦a1≦0.9, 0 a2≦0.9, and 0<a1+a2<1.0.

Also preferably, the polymer comprising recurring units of at least onetype selected from recurring units (a1) and (a2) having a carboxyland/or phenolic hydroxyl group substituted with an acid labile group,represented by the general formula (2), has further copolymerizedtherein recurring units of at least one type selected from sulfoniumsalt units (b1) to (b3), as represented by the general formula (3).

Herein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl, R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH,R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylenegroup or phenylene group, which may contain a carbonyl (—CO—), ester(—COO—), ether (—O—), or hydroxyl moiety, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷,R⁰²⁹, R⁰³⁰, and R⁰³¹ are each independently a straight, branched orcyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester or ethermoiety, a C₆-C₁₂ aryl group, a C₇-C₂₀ aralkyl group, or a thiophenylgroup, A¹ is a single bond, -A⁰-C(═O)—O—, -A⁰-O— or -A⁰-O—C(═O)—, A⁰ isa straight, branched or cyclic C₁-C₁₂ alkylene group which may contain acarbonyl, ester or ether moiety, A² is hydrogen, CF₃ or carbonyl, Z¹ isa single bond, methylene, ethylene, phenylene, fluorinated phenylene,—O—R⁰³²—, or —C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is a straight,branched or cyclic C₁-C₆ alkylene, phenylene, fluorinated phenylene,trifluoromethyl-substituted phenylene or alkenylene group, which maycontain a carbonyl, ester, ether or hydroxyl moiety, M⁻ is anon-nucleophilic counter ion, b1, b2 and b3 are numbers in the range:0≦b1≦0.3, 0≦b≦0.3, 0≦b3≦0.3, and 0<b1+b2+b3≦0.3.

The resist composition may further comprise at least one of an organicsolvent, basic compound, dissolution regulator, and surfactant.

Preferably, 0.1 to 50 parts by weight of the additive polymer is presentper 100 parts by weight of the base polymer.

In another aspect, the invention provides a pattern forming processcomprising the steps of applying the resist composition defined aboveonto a substrate to form a coating, baking, exposing the coating tohigh-energy radiation, and developing the exposed coating in adeveloper. Typically, the high-energy radiation is electron beam or softx-ray of wavelength 3 to 15 nm.

Advantageous Effects of Invention

The photoresist film formed using the resist composition of theinvention is effective for minimizing the emission of outgassingcomponents from the resist film during the EUV lithography. Since theresist film has a hydrophilic surface, it is effective for suppressingformation of blob defects after development.

DESCRIPTION OF EMBODIMENTS

The singular forms “a,” “an” and “the” include plural referents unlessthe context clearly dictates otherwise. “Optional” or “optionally” meansthat the subsequently described event or circumstances may or may notoccur, and that description includes instances where the event orcircumstance occurs and instances where it does not.

As used herein, the terminology “(meth)acrylic acid” or “(meth)acrylate”refers collectively to acrylic and methacrylic acid or acrylate andmethacrylate. The terminology “C_(x)-C_(y)”, as applied to a particularunit, such as, for example, a chemical compound or a chemicalsubstituent group, means having a carbon atom content of from “x” carbonatoms to “y” carbon atoms per such unit.

The abbreviations have the following meaning.

EB: electron beamEUV: extreme ultravioletPAG: photoacid generatorPEB: post-exposure bakeLER: line edge roughnessLWR: line width roughnessMw: weight average molecular weightMn: number average molecular weightMw/Mn: dispersity or average molecular weight distributionGPC: gel permeation chromatography

Making efforts to overcome the outstanding problems, the inventors havefound that a resist composition obtained by blending an ordinary basepolymer which turns alkali soluble under the action of acid with anotherpolymer comprising recurring units derived from afluorosulfonamide-substituted styrene and recurring units derived from astilbene, styrylnaphthalene, dinaphthylethylene, acenaphthylene, indene,benzofuran, or benzothiophene derivative in copolymerized form iseffective for suppressing the emission of outgassing components from theresist film during exposure in vacuum by the EUV lithography. Because oftheir robustness and high density, the recurring units derived from afluorosulfonamide-substituted styrene and the recurring units derivedfrom a stilbene, styrylnaphthalene, dinaphthylethylene, acenaphthylene,indene, benzofuran, or benzothiophene derivative are effective forshutting off outgassing from the photoresist film. The other polymerwill segregate on the surface of the resist film after spin coating.

Additive Polymer

One embodiment of the invention is a resist composition characterized bycomprising a polymer capable of increasing alkali solubility under theaction of acid as base resin, which is often referred to as “basepolymer”, and a polymer having copolymerized therein recurring unitsderived from a fluorosulfonamide-substituted styrene and recurring unitsderived from at least one monomer selected from stilbene,styrylnaphthalene, dinaphthylethylene, acenaphthylene, indene,benzofuran, and benzothiophene derivatives as polymeric additive, whichis often referred to as “additive polymer.” Typically, the additivepolymer has the general formula (1).

Herein R¹ is a single bond or a straight or branched C₁-C₄ alkylenegroup. R² is fluorine, or a straight, branched or cyclic C₁-C₆ alkyl,phenyl or alkyl-substituted phenyl group which contains at least onefluorine atom. R³ and R⁴ are each independently selected from amonghydrogen, hydroxyl, straight, branched or cyclic C₁-C₁₀ alkyl, alkoxy,acyloxy, C₂-C₆ alkenyl, C₆-C₁₀ aryl, cyano, nitro, amino and halogen. X¹and X² each are phenylene or naphthylene, and m is 1 or 2. R⁵ and R⁶ areeach independently selected from among hydrogen, halogen, straight orbranched C₁-C₄ alkyl, alkoxy, acyloxy, hydroxyl, carboxyl, andalkoxycarbonyl. M is a methylene group, oxygen atom or sulfur atom. Thesubscripts p, q−1, q−2 and q−3 are numbers in the range: 0<p<1.0,0≦(q−1)<1.0, 0 (q−2)<1.0, 0 (q−3)<1.0, and 0<(q−1)+(q−2)+(q−3)<1.0.

Examples of the group R² include F, CF₃, C₂F₅, CF₂CHF₂, CF₂CF₂CF₃,CF₂CF₂CF₂CF₃, and groups of the following formulae.

Herein x is an integer of 1 to 5, and y is 1 or 2.

The resist composition having the polymer comprising recurring units offormula (1) added thereto is coated to form a photoresist film. Thephotoresist film is characterized in that a polymeric surfactant havingcopolymerized therein recurring units derived from afluorosulfonamide-substituted styrene and recurring units derived fromat least one monomer selected from stilbene, styrylnaphthalene,dinaphthylethylene, acenaphthylene, indene, benzofuran, andbenzothiophene derivatives is present on the film surface. The polymericsurfactant segregates on the photoresist film surface at the end ofphotoresist coating and functions to suppress the release of outgassingcomponents from the resist film and to minimize defects in the resistpattern after development.

While the recurring units derived from a fluorosulfonamide-substitutedstyrene are represented by units (p) in formula (1), examples of themonomer from which recurring units (p) are derived are shown below, butnot limited thereto.

Examples of the monomer from which units (q−1) to be copolymerized withrecurring units (p) in formula (1) are derived are shown below, but notlimited thereto.

Examples of the monomer from which units (q−2) are derived are shownbelow, but not limited thereto.

Examples of the monomer from which units (q−3) are derived are shownbelow, but not limited thereto.

Where a monomer has a hydroxyl group, the hydroxyl group may be replacedby an acetyl, acetal or similar group at the monomer stage, and thepolymerization be followed by deprotection reaction to restore thehydroxyl group. Where the hydroxyl group is replaced by an acetyl group,the polymerization may be followed by alkaline hydrolysis to deprotectthe acetyl group into a hydroxyl group. Where the hydroxyl group isreplaced by an acid labile group such as acetal, deprotection viahydrolysis with an acid catalyst may be carried out to restore ahydroxyl group.

In the additive polymer, recurring units (p), that is, alkali-solublestyrene units having fluorosulfonamide are essential, while recurringunits of at least one type selected from recurring units (q−1) derivedfrom stilbene, styrylnaphthalene, and dinaphthylethylene derivatives,recurring units (q−2) derived from acenaphthylene derivatives, andrecurring units (q−3) derived from indene, benzofuran, andbenzothiophene derivatives are also essentially incorporated to enhancethe effect of shutting off outgassing components from the photoresistfilm during EUV exposure. Of the recurring units (q−1), (q−2) and (q−3),copolymerization of acenaphthylene units (q−2) is most effective forsuppressing generation of outgassing components.

Besides the recurring units (p), (q−1), (q−2) and (q−3) in formula (1),recurring units (r) having fluorine may be copolymerized. The recurringunits (r) are typically recurring units (r−1) having anα-trifluoromethyl alcohol group and recurring units (r−2) having afluoroalkyl group.

Examples of the monomer from which recurring units (r−1) having anα-trifluoromethyl alcohol group are derived are given below.

Examples of the monomer from which recurring units (r−2) having afluoroalkyl group are derived are given below.

In addition to the recurring units (p), (q−1), (q−2), (q−3) in formula(1) and units (r), the polymer to be added to the resist composition mayhave further copolymerized therein recurring units (s) having a carboxylgroup for the purposes of improving alkali solubility and rendering theresist film after development more hydrophilic.

Examples of the recurring units (s) having a carboxyl group are givenbelow.

Besides the recurring units (p), (q−1), (q−2), (q−3), (r) and (s), it isacceptable to copolymerize recurring units (t) derived from at least onemonomer selected from among styrene, vinylnaphthalene, vinylanthracene,vinylpyrene, and vinylbiphenyl derivatives.

While the additive polymer comprises the recurring units (p), (q−1),(q−2), and (q−3) and optionally, the recurring units (r), (s) and (t),their molar fraction is in the following range:

0<p<1.0, 0≦(q−1)<1.0, 0≦(q−2)<1.0, 0≦(q−3)<1.0, 0<(q−1)+(q−2)+(q−3)<1.0,0≦r≦0.6, 0≦s≦0.6, 0≦t≦0.6, 0≦a1≦0.6, 0≦a2≦0.6,preferably 0.2≦p≦0.95, 0≦(q−1)≦0.9, 0≦(q−2)≦0.9, 0≦(q−3)≦0.9,0.05≦(q−1)+(q−2)+(q−3) 0.8, 0≦r≦0.5, 0≦s≦0.5, 0≦t 0.5, 0≦a1≦0.5,0≦a2≦0.5, andmore preferably 0.3≦p≦0.9, 0≦(q−1)≦0.8, 0≦(q−2)≦0.8, 0≦(q−3) 0.8, 0.1(q−1)+(q−2)+(q−3)≦0.7, 0≦r≦0.4, 0≦s≦0.4, 0≦t≦0.4, 0≦a1≦0.4, 0≦a2≦<0.4.

It is noted that the additive polymer may have further copolymerizedtherein recurring units (a1) and (a2) having an acid labile group, whichwill be described later in conjunction with the base polymer.

The additive polymer should preferably have a weight average molecularweight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000to 30,000, as measured by GPC versus polystyrene standards. With too lowa Mw, the resist composition may become less heat resistant. A polymerwith too high a Mw may lose alkaline solubility and give rise to afooting phenomenon after pattern formation.

Base Resin

The polymer serving as base resin in the resist composition of theinvention essentially comprises recurring units having an acid labilegroup. Preferably, the recurring units having an acid labile groupinclude recurring units (a1) of (meth)acrylate having an acid labilegroup R¹¹ substituted thereon and recurring units (a2) of hydroxystyrenehaving an acid labile group R¹³ substituted thereon, as represented bythe general formula (2).

Herein R¹⁰ and R¹² are each independently hydrogen or methyl, R¹¹ andR¹³ each are an acid labile group, Y¹ is a single bond, a C₁-C₁₂ linkinggroup having at least one of an ester (—COO—) moiety, lactone ring,phenylene moiety and naphthylene moiety, a phenylene group or anaphthylene group, Y² is a single bond, ester (—COO—) group or amide(—CONH—) group, subscripts a1 and a2 are numbers in the range: 0≦a1≦0.9,0≦a2≦0.9, and 0<a1+a2<1.0.

Notably, the recurring units having an acid labile group may becopolymerized with the additive polymer of formula (1), as alluded toabove.

Examples of the monomer from which recurring units (a1) are derived aregiven below.

Herein R¹⁰ is hydrogen or methyl and R¹¹ is an acid labile group.

Examples of the monomer from which recurring units (a2) are derived aregiven below.

Herein R¹² is hydrogen or methyl and R¹³ is an acid labile group.

The acid labile groups represented by R¹¹ and R¹³ in formula (2) may beselected from a variety of such groups. The acid labile groups may bethe same or different and preferably include groups of the followingformulae (A-1) to (A-3).

In formula (A-1), R³⁰ is a tertiary alkyl group of 4 to 20 carbon atoms,preferably 4 to 15 carbon atoms, a trialkylsilyl group in which eachalkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (A-3). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl.

Exemplary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl,and 5-methyl-2-oxooxolan-5-yl. Letter A1 is an integer of 0 to 6.

In formula (A-2), R³¹ and R³² are hydrogen or straight, branched orcyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbonatoms. Exemplary alkyl groups include methyl, ethyl, propyl, isopropyl,n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl,and n-octyl. R³³ is a monovalent hydrocarbon group of 1 to 18 carbonatoms, preferably 1 to 10 carbon atoms, which may contain a heteroatomsuch as oxygen, examples of which include straight, branched or cyclicalkyl groups and substituted forms of such alkyl groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino, alkylaminoor the like. Illustrative examples of the substituted alkyl groups areshown below.

A pair of R³¹ and R³², R³¹ and R³³, or R³² and R³³ may bond together toform a ring with the carbon and oxygen atoms to which they are attached.Each of R³¹, R³² and R³³ is a straight or branched alkylene group of 1to 18 carbon atoms, preferably 1 to 10 carbon atoms when they form aring, while the ring preferably has 3 to 10 carbon atoms, morepreferably 4 to 10 carbon atoms.

Examples of the acid labile groups of formula (A-1) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethyl cyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

Also included are substituent groups having the formulae (A-1)-1 to(A-1)-10.

Herein R³⁷ is each independently a straight, branched or cyclic C₁-C₁₀alkyl group or C₆-C₂₀ aryl group. R³⁸ is hydrogen or a straight,branched or cyclic C₁-C₁₀ alkyl group. R³⁹ is each independently astraight, branched or cyclic C₂-C₁₀ alkyl group or C₆-C₂₀ aryl group. A1is an integer of 0 to 6.

Of the acid labile groups of formula (A-2), the straight and branchedones are exemplified by the following groups having formulae (A-2)-1 to(A-2)-69.

Of the acid labile groups of formula (A-2), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Other examples of acid labile groups include those of the followingformula (A-2a) or (A-2b) while the polymer may be crosslinked within themolecule or between molecules with these acid labile groups.

Herein R⁴⁰ and R⁴¹ each are hydrogen or a straight, branched or cyclicC₁-C₈ alkyl group, or R⁴⁰ and R⁴¹, taken together, may form a ring withthe carbon atom to which they are attached, and Ru and R⁴¹ are straightor branched C₁-C₈ alkylene groups when they form a ring. R⁴² is astraight, branched or cyclic C₁-C₁₀ alkylene group. Each of B1 and D1 is0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and C1is an integer of 1 to 7. “A” is a (C1+1)-valent aliphatic or alicyclicsaturated hydrocarbon group, aromatic hydrocarbon group or heterocyclicgroup having 1 to 50 carbon atoms, which may be separated by aheteroatom or in which some hydrogen atoms attached to carbon atoms maybe substituted by hydroxyl, carboxyl, carbonyl groups or fluorine atoms.“B” is —CO—O—, —NHCO—O— or —NHCONH—

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkyltriyl and alkyltetrayl groups,and C₆-C₃₀ arylene groups, which may be separated by a heteroatom or inwhich some hydrogen atoms attached to carbon atoms may be substituted byhydroxyl, carboxyl, acyl groups or halogen atoms. The subscript C1 ispreferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (A-2a) and (A-2b) areexemplified by the following formulae (A-2)-70 through (A-2)-77.

In formula (A-3), e, e and e each are a monovalent hydrocarbon group,typically a straight, branched or cyclic C₁-C₂₀ alkyl, straight,branched or cyclic C₂-C₂₀ alkenyl or C₆-C₂₀ aryl group, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Apair of R³⁴ and e, R³⁴ and R³⁶, or R³⁵ and R³⁶ may bond together to forma C₃-C₂₀ aliphatic ring with the carbon atom to which they are attached.

Exemplary tertiary alkyl groups of formula (A-3) include tert-butyl,triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, andtert-amyl.

Other exemplary tertiary alkyl groups include those of the followingformulae (A-3)-1 to (A-3)-18.

Herein R⁴³ is each independently a straight, branched or cyclic C₁-C₈alkyl group or C₆-C₂₀ aryl group, typically phenyl, R⁴⁴ and R⁵⁶ each arehydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group, and R⁴⁵is a C₆-C₂₀ aryl group, typically phenyl.

The polymer may be crosslinked within the molecule or between moleculeswith groups having R⁴⁷ which is a di- or multi-valent alkylene orarylene group, as shown by the following formulae (A-3)-19 and (A-3)-20.

Herein R⁴³ is as defined above, R⁴⁷ is a straight, branched or cyclicC₁-C₂₀ alkylene group or arylene group, typically phenylene, which maycontain a heteroatom such as oxygen, sulfur or nitrogen, and E1 is aninteger of 1 to 3.

Of recurring units having acid labile groups of formula (A-3), recurringunits (a1) of (meth)acrylate having an exo-form structure represented bythe formula (A-3)-21 are preferred.

Herein, R¹⁰ and a1 are as defined above. R^(c3) is a straight, branchedor cyclic C₁-C₈ alkyl group or an optionally substituted C₆-C₂₀ arylgroup. R^(c4) to R^(c9), R^(c12) and R^(c13) are each independentlyhydrogen or a monovalent C₁-C₁₅ hydrocarbon group which may contain aheteroatom. R^(c10) and R^(c11) each are hydrogen or a monovalent C₁-C₁₅hydrocarbon group which may contain a heteroatom. Alternatively, a pairof R^(c4) and R^(c5), R^(c6) and R^(c8), R^(c6) and R^(c9), R^(c7) andR^(c9), R^(c7) and R^(c13), R^(c8) and R^(c12), R^(c10) and R^(c11), orR^(c11) and R^(c12), taken together, may form a ring, and in that event,each ring-forming R is a divalent C₁-C₁₅ hydrocarbon group which maycontain a heteroatom. Also, a pair of R^(c4) and R^(c13), R^(c10) andR^(c13), or R^(c6) and R^(c8) which are attached to vicinal carbon atomsmay bond together directly to form a double bond. The formula alsorepresents an enantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by formula (A-3)-21 are derived are described inU.S. Pat. No. 6,448,420 (JP-A 2000-327633). Illustrative non-limitingexamples of suitable monomers are given below.

Also included in the recurring units having acid labile groups offormula (A-3) are recurring units (a1) of (meth)acrylate havingfurandiyl, tetrahydrofurandiyl or oxanorbornanediyl as represented bythe following formula (A-3)-22.

Herein, R¹⁰ and a1 are as defined above. R^(c14) and R^(c15) are eachindependently a monovalent, straight, branched or cyclic C₁-C₁₀hydrocarbon group, or R^(c14) and R^(c15), taken together, may form analiphatic hydrocarbon ring with the carbon atom to which they areattached. R^(c16) is a divalent group selected from furandiyl,tetrahydrofurandiyl and oxanorbornanediyl. R^(c17) is hydrogen or amonovalent, straight, branched or cyclic C₁-C₁₀ hydrocarbon group whichmay contain a heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl are derived are shown below. Note that Me is methyland Ac is acetyl.

In the recurring unit (a1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-23.

Herein R²³⁻¹ is hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl, alkoxycarbonyl,C₆-C₁₀ aryl, halogen, or cyano group, and m23 is an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-23 are given below.

In the recurring unit (a1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-24.

Herein R²⁴⁻¹ and R²⁴⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, C₆-C₁₀ aryl, halogen, or cyano group; R ishydrogen, a straight, branched or cyclic C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl,C₂-C₁₂ alkynyl, or C₆-C₁₀ aryl group, which may contain an oxygen orsulfur atom; R²⁴⁻³, R²⁴⁻⁴ R²⁴⁻⁵ and R²⁴⁻⁶ each are hydrogen, or a pairof R²⁴⁻³ and R²⁴⁻⁴, R²⁴⁻⁴ and R²⁴⁻⁵, or R²⁴⁻⁵ and R²⁴⁻⁶ may bondtogether to form a benzene ring; m24 and n24 each are an integer of 1 to4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-24 are given below.

In the recurring unit (a1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-25.

Herein R²⁵⁻¹ is each independently hydrogen or a straight, branched orcyclic C₁-C₆ alkyl group, and in case m25 is 2 or more, R²⁵⁻¹ may bondtogether to form a non-aromatic ring of 2 to 8 carbon atoms; the circledenotes a link between carbons C_(A) and C_(B), selected from amongethylene, propylene, butylene and pentylene; R²⁵⁻¹ is not hydrogen whenthe circle denotes ethylene or propylene; R²⁵⁻² is C₁-C₄ alkyl, alkoxy,alkanoyl, alkoxycarbonyl, hydroxyl, nitro, C₆-C₁₀ aryl, halogen, orcyano group; R is as defined above; m25 and n25 each are an integer of 1to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-25 are given below.

In the recurring unit (a1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-26.

Herein R²⁶⁻¹ and R²⁶⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, nitro, C₆-C₁₀ aryl, halogen, or cyano group; Ris as defined above; and m26 and n26 each are an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-26 are given below.

In the recurring unit (a1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-27.

Herein R²⁷⁻¹ and R²⁷⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, C₆-C₁₀ aryl, halogen, or cyano group; R is asdefined above; J is methylene, ethylene, vinylene or —CH₂—S—; and m27and n27 each are an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-27 are given below.

In the recurring unit (a1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-28.

Herein R²⁸⁻¹ and R²⁸⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, C₆-C₁₀ aryl, halogen, or cyano group; R is asdefined above; K is carbonyl, ether, sulfide, —S(═O)— or —S(═O)₂—; andm28 and n28 each are an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-28 are given below.

Also included are fluorinated acid labile groups as shown below.

In a preferred embodiment of the polymer serving as base resin,recurring units (c) having an adhesive group may be copolymerized withthe recurring units (a1) and (a2) having an acid labile group,represented by formula (2), for the purposes of improving compatibilitywith other components and suppressing a film thickness loss on theresist surface. Suitable adhesive groups include hydroxyl, carboxyl,lactone ring, carbonyl, carbonate, ester, ether, amide, sulfonamide,cyano, sulfonic acid ester, lactam and the like. The preferred recurringunits (c) are those having a phenolic hydroxyl group which has asensitizing effect in the EB and EUV lithography. The recurring units(c) having a phenolic hydroxyl group are typically selected from units(c1) to (c9) represented by the general formula (4).

Herein R²¹ is each independently hydrogen or methyl. V¹, V² and V⁵ eachare a single bond or —C(═O)—O—R²³—, V³ and V⁴ each are —C(═O)—O—R²⁴—,wherein R²³ and R²⁴ each are a single bond or a straight, branched orcyclic C₁-C₁₀ alkylene group which may contain an ether or ester moiety.R²² is each independently hydrogen, or a C₁-C₄ straight or branchedalkyl, alkoxy, cyano, alkoxycarbonyl, acyloxy or acyl group. W¹ and W²each are methylene or ethylene, W³ is methylene, oxygen or sulfur, W⁴and W⁵ each are CH or nitrogen, and u and t each are 1 or 2.

Examples of the monomers from which the recurring units (c1) to (c9)having a phenolic hydroxyl group are derived are given below.

Examples of the monomers from which the recurring units (c) having anadhesive group such as hydroxyl (exclusive of phenolic hydroxyl),lactone ring, ether, ester, carbonyl, cyano, sulfonic acid ester,sulfonamide group, cyclic —O—C(═O)—S— or —O—C(═O)—NH— group are derivedare given below.

Where a monomer has a hydroxyl group, the hydroxyl group may be replacedby an acetal group susceptible to deprotection with acid, typicallyethoxyethoxy, prior to polymerization, and the polymerization befollowed by deprotection with weak acid and water. Alternatively, thehydroxy group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In a more preferred embodiment, the polymer serving as base resin hasfurther copolymerized therein recurring units (d) selected from units(d1) to (d5) of indene, acenaphthylene, chromone, coumarin, andnorbornadiene, or derivatives thereof, represented by the followingformula (5).

Herein R²⁵ is each independently hydrogen, a C₁-C₃₀ alkyl, haloalkyl,alkoxy, alkanoyl or alkoxycarbonyl group, C₆-C₁₀ aryl group, halogen, or1,1,1,3,3,3-hexafluoro-2-propanol group, and W⁶ is methylene, oxygen orsulfur. As used herein, the term “haloalkyl” refers to alkyl in whichsome or all hydrogen atoms are substituted by halogen.

Examples of suitable monomers from which recurring units (d1) to (d5) ofindene, acenaphthylene, chromone, coumarin, and norbornadienederivatives are derived are given below.

In a further embodiment, an acid generator (b) in the form of an oniumsalt having polymerizable olefin may be copolymerized with the foregoingmonomers. JP-A H04-230645, JP-A 2005-084365, and JP-A 2006-045311disclose sulfonium salts having polymerizable olefin capable ofgenerating a specific sulfonic acid and similar iodonium salts. JP-A2006-178317 discloses a sulfonium salt having sulfonic acid directlyattached to the main chain.

In this embodiment, the polymer may have further copolymerized thereinrecurring units (b1) to (b3) having a sulfonium salt, represented by thefollowing formula (3). Sometimes, units (b1) to (b3) are collectivelyreferred to as units (b).

Herein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl. R is a singlebond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, wherein Y is oxygen or NH,and R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl (—CO—),ester (—COO—), ether (—O—) or hydroxyl moiety. R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶,R⁰²⁷, R⁰²⁹, R⁰³⁰, and R⁰³¹ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether moiety, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group. A¹is a single bond, -A⁰-C(═O)—O—, -A⁰-O— or -A⁰-O—C(═O)—, wherein A⁰ is astraight, branched or cyclic C₁-C₁₂ alkylene group which may contain acarbonyl, ester or ether moiety. A² is hydrogen, CF₃ or carbonyl. Z¹ isa single bond, methylene, ethylene, phenylene, fluorinated phenylene,—O—R⁰³²—, or —C(═O)—Z²—R⁰³²—. Z is oxygen or NH. R⁰³² is a straight,branched or cyclic C₁-C₆ alkylene, phenylene, fluorinated phenylene,trifluoromethyl-substituted phenylene, or alkenylene group, which maycontain a carbonyl, ester, ether or hydroxyl moiety. M is anon-nucleophilic counter ion. Molar fractions b1, b2 and b3 are in therange of 0≦b≦0.3, 0≦b2≦0.3, 0≦b3≦0.3, and 0≦b1+b2+b3≦0.3.

Examples of the monomer from which the sulfonium salt-containingrecurring units (b1) are derived are shown below.

Herein M⁻ is a non-nucleophilic counter ion.

Examples of the non-nucleophilic counter ion represented by M⁻ includehalide ions such as chloride and bromide ions; fluoroalkylsulfonate ionssuch as triflate, 1,1,1-trifluoroethanesulfonate, andnonafluorobutanesulfonate; arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such asmesylate and butanesulfonate; imidates such asbis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide andbis(perfluorobutylsulfonyl)imide; methidates such astris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Other non-nucleophilic counter ions include sulfonates having fluorinesubstituted at α-position as represented by the general formula (K-1)and sulfonates having fluorine substituted at α- and β-positions asrepresented by the general formula (K-2).

In formula (K-1), R¹⁰² is hydrogen, or a straight, branched or cyclicC₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl group, whichmay have an ether, ester, carbonyl moiety, lactone ring or fluorine. Informula (K-2), R¹⁰³ is hydrogen, or a straight, branched or cyclicC₁-C₃₀ alkyl or acyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl oraryloxy group, which may have an ether, ester, carbonyl moiety orlactone ring.

Examples of the monomer from which the sulfonium salt-containingrecurring units (b2) are derived are shown below.

Examples of the monomer from which the sulfonium salt-containingrecurring units (b3) are derived are shown below.

The attachment of an acid generator to the polymer main chain iseffective in restraining acid diffusion, thereby preventing a reductionof resolution due to blur by acid diffusion. Also edge roughness (LER orLWR) is improved since the acid generator is uniformly dispersed.

There have been described the additive polymer of formula (1) aspolymeric additive for modifying the resist film surface and the acidlabile group-containing polymer of formula (2) as base resin. Thesepolymers may be synthesized by any desired methods, for example, bydissolving suitable monomers selected from the monomers to formrecurring units (p), (q), (r), (s), and (t) or recurring units (a) to(d) in an organic solvent, adding a radical polymerization initiatorthereto, and effecting heat polymerization.

Examples of the organic solvent which can be used for polymerizationinclude toluene, benzene, tetrahydrofuran, diethyl ether and dioxane.Examples of the polymerization initiator used herein include2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxyacenaphthylene is copolymerized, an alternative method ispossible. Specifically, acetoxystyrene or acetoxyvinylnaphthalene isused instead of hydroxyacenaphthylene, and after polymerization, theacetoxy group is deprotected by alkaline hydrolysis as mentioned above,for thereby converting the polymer product to polyhydroxystyrene orhydroxypolyvinylnaphthalene. For alkaline hydrolysis, a base such asaqueous ammonia or triethylamine may be used. The reaction temperatureis −20° C. to 100° C., preferably 0° C. to 60° C., and the reaction timeis 0.2 to 100 hours, preferably 0.5 to 20 hours.

In the base polymer, recurring units (a) to (d) may be incorporated inthe following molar fraction:

0≦a1≦0.9, 0≦a2≦0.9, 0<a1+a2<1.0, preferably 0≦a1≦0.8, 0≦a≦0.8,0.1≦a1+a≦0.8, and more preferably 0≦a1≦0.7, 0≦a2≦0.7, 0.2≦a1+a2≦0.7;0≦b1≦0.3, 0≦b≦0.3, 0≦b3≦0.3, and0≦b1+b2+b3≦0.3, and when incorporated, 0<b1+b2+b3≦0.3;0≦c<1.00, preferably 0<c 0.9, and more preferably 0<c 0.8;0≦d≦0.5, preferably 0≦d≦0.4, and more preferably 0≦d≦0.3;provided that a1+a2+b1+b2+b3+c+d=1.0.

The meaning of a+b+c=1, for example, is that in a polymer comprisingrecurring units (a), (b), and (c), the sum of recurring units (a), (b),and (c) is 100 mol % based on the total amount of entire recurringunits. The meaning of a+b+c<1 is that the sum of recurring units (a),(b), and (c) is less than 100 mol % based on the total amount of entirerecurring units, indicating the inclusion of other recurring units.

The base polymer should preferably have a weight average molecularweight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000to 30,000, as measured by GPC versus polystyrene standards. With too lowa Mw, the resist composition may become less heat resistant. A polymerwith too high a Mw may lose alkaline solubility and give rise to afooting phenomenon after pattern formation.

If a multi-component polymer has a wide molecular weight distribution ordispersity (Mw/Mn), which indicates the presence of lower and highermolecular weight polymer fractions, there is a possibility that foreignmatter is left on the pattern or the pattern profile is degraded. Theinfluences of molecular weight and dispersity become stronger as thepattern rule becomes finer. Therefore, the multi-component polymershould preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0,especially 1.0 to 1.5, in order to provide a resist composition suitablefor micropatterning to a small feature size.

For both the alkali-soluble polymer and the base polymer, a mixture oftwo or more polymers which differ in compositional ratio, molecularweight or dispersity is acceptable.

The resist composition is based on a blend of an alkali-soluble polymeror additive polymer comprising recurring units (p) and (q−1), (q−2) or(q−3), optionally (r), (s) and/or (t) and further optionally (a1) and/or(a2) which segregates on the resist film surface after coating andfunctions to suppress outgassing from the resist film, to preventformation of bridge and blob defects, and to minimize LWR, and an acidlabile group-containing polymer or base polymer comprising recurringunits (a1), (a2), (b1), (b2), (b3), (c) and (d) which turns soluble inalkaline developer under the action of acid. Typically the additivepolymer (i.e., surface segregating polymeric additive) is blended in anamount of 0.1 to 50 parts, preferably 0.2 to 30 parts, and morepreferably 0.2 to 20 parts by weight per 100 parts by weight of the basepolymer. Also typically, the surface segregating polymeric additivealone has an alkaline dissolution rate of 0.001 to 100,000 nm/s,preferably 0.01 to 50,000 nm/s, and more preferably 0.1 to 20,000 nm/s.Although the additive polymer may have a very low alkaline dissolutionrate when units (a1) or (a2) are copolymerized therein, the alkalinedissolution rate can increase in response to acid because of inclusionof units (a1) or (a2).

Resist Composition

The resist composition may include an acid generator in order for thecomposition to function as a chemically amplified positive resistcomposition. Typical of the acid generator used herein is a photoacidgenerator (PAG) capable of generating an acid in response to actiniclight or radiation. It is any compound capable of generating an acidupon exposure to high-energy radiation. Suitable PAGs include sulfoniumsalts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, andoxime-O-sulfonate acid generators. The acid generators may be used aloneor in admixture of two or more. Exemplary acid generators are describedin U.S. Pat. No. 7,537,880 (JP-A 2008-111103, paragraphs [0122] to[0142]). In the embodiment wherein a polymer having recurring units (b)copolymerized therein is used as the base resin, the PAG may be omitted.

The resist composition may further comprise an organic solvent, basiccompound, dissolution regulator, surfactant, and acetylene alcohol,alone or in combination.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880).Specifically, exemplary solvents include ketones such as cyclohexanoneand methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate; and lactones such as γ-butyrolactone, and mixtures thereof.

Exemplary basic compounds are described in JP-A 2008-111103, paragraphs[0146] to [0164], for example, primary, secondary and tertiary aminecompounds, specifically amine compounds having a hydroxyl, ether, ester,lactone, cyano or sulfonate group. Exemplary surfactants are describedin JP-A 2008-111103, paragraphs [0165] to [0166]. Exemplary dissolutionregulators are described in JP-A 2008-122932 (US 2008090172), paragraphs[0155] to [0178], and exemplary acetylene alcohols in paragraphs [0179]to [0182]. Also useful are quenchers of polymer type as described inJP-A 2008-239918. The polymeric quencher segregates at the resistsurface after coating and thus enhances the rectangularity of resistpattern. When a protective film is applied as is often the case in theimmersion lithography, the polymeric quencher is also effective forpreventing any film thickness loss of resist pattern or rounding ofpattern top.

An appropriate amount of the acid generator used is 0.01 to 100 parts,and preferably 0.1 to 80 parts. An appropriate amount of the organicsolvent used is 50 to 10,000 parts, especially 100 to 5,000 parts. Thedissolution regulator may be blended in an amount of 0 to 50 parts,preferably 0 to 40 parts, the basic compound in an amount of 0 to 100parts, preferably 0.001 to 50 parts, and the surfactant in an amount of0 to 10 parts, preferably 0.0001 to 5 parts. All amounts are expressedin parts by weight relative to 100 parts by weight of the base resin.

Process

The resist composition, typically chemically amplified positive resistcomposition comprising an additive polymer of formula (1), an acidlabile group-containing polymer of formula (2), an acid generator, and abasic compound in an organic solvent is used in the fabrication ofvarious integrated circuits. Pattern formation using the resistcomposition may be performed by well-known lithography processes. Theprocess generally involves coating, prebake, exposure, bake (PEB), anddevelopment. If necessary, any additional steps may be added.

The resist composition is first applied onto a substrate on which anintegrated circuit is to be formed (e.g., Si, SiO₂, SiN, SiON, TiN, WSi,BPSG, SOG, or organic antireflective coating) or a substrate on which amask circuit is to be formed (e.g., Cr, CrO, CrON, MoSi, or SiO₂) by asuitable coating technique such as spin coating, roll coating, flowcoating, dip coating, spray coating or doctor coating. The coating isprebaked on a hot plate at a temperature of 60 to 150° C. for 10 secondsto 30 minutes, preferably 80 to 120° C. for 30 seconds to 20 minutes.The resulting resist film is generally 0.1 to 2.0 μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, x-ray, excimer laser light, γ-ray,synchrotron radiation or EUV (soft x-ray), directly or through a mask.The exposure dose is preferably about 1 to 200 mJ/cm², more preferablyabout 10 to 100 mJ/cm², or 0.1 to 100 μC/cm², more preferably 0.5 to 50μC/cm². The resist film is further baked (PEB) on a hot plate at 60 to150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed in a developer in the form of anaqueous base solution for 3 seconds to 3 minutes, preferably 5 secondsto 2 minutes by conventional techniques such as dip, puddle or spraytechniques. Suitable developers are 0.1 to 10 wt %, preferably 2 to 10wt %, more preferably 2 to 8 wt % aqueous solutions oftetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide(TEAH), tetrapropylammonium hydroxide (TPAH) and tetrabutylammoniumhydroxide (TBAH). The resist film in the exposed area is dissolved inthe developer whereas the resist film in the unexposed area is notdissolved. In this way, the desired positive pattern is formed on thesubstrate. It is appreciated that the resist composition of theinvention is best suited for micro-patterning using such high-energyradiation as EB, EUV (soft x-ray), x-ray, γ-ray and synchrotronradiation among others.

Although TMAH aqueous solution is generally used as the developer, TEAH,TPAH and TBAH having a longer alkyl chain are effective in inhibitingthe resist film from being swollen during development and thuspreventing pattern collapse. JP 3429592 describes an example using anaqueous TBAH solution for the development of a polymer comprisingrecurring units having an alicyclic structure such as adamantanemethacrylate and recurring units having an acid labile group such ast-butyl methacrylate, the polymer being water repellent due to theabsence of hydrophilic groups.

The TMAH developer is most often used as 2.38 wt % aqueous solution,which corresponds to 0.26N. The TEAH, TPAH, and TBAH aqueous solutionsshould preferably have an equivalent normality. The concentration ofTEAH, TPAH, and TBAH that corresponds to 0.26N is 3.84 wt %, 5.31 wt %,and 6.78 wt %, respectively.

When a pattern with a line size of 32 nm or less is resolved by the EBand EUV lithography, there arises a phenomenon that lines become wavy,lines merge together, and merged lines collapse. It is believed thatthis phenomenon occurs because lines are swollen in the developer andthe thus expanded lines merge together. Since the swollen linescontaining liquid developer are as soft as sponge, they readily collapseunder the stress of rinsing. For this reason, the developer using along-chain alkyl developing agent is effective for preventing film swelland hence, pattern collapse.

Alternatively, a negative tone pattern may be formed by organic solventdevelopment. The organic solvent used as the developer is preferablyselected from 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, phenyl acetate, propyl formate, butyl formate, isobutylformate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate. Theseorganic solvents may be used alone or in admixture of two or more.

At the end of organic solvent development, the resist film is rinsed. Asthe rinsing liquid, a solvent which is miscible with the developer anddoes not dissolve the resist film is preferred. Suitable solventsinclude alcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12carbon atoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alkanes of 6 to 12 carbonatoms include hexane, heptane, octane, nonane, decane, undecane,dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-amylether, and di-n-hexyl ether. The solvents may be used alone or inadmixture. Besides the foregoing solvents, aromatic solvents may beused, for example, toluene, xylene, ethylbenzene, isopropylbenzene,tert-butylbenzene and mesitylene.

EXAMPLE

Examples and Comparative Examples are given below for furtherillustrating the invention, but they should not be construed as limitingthe invention thereto. Mw is a weight average molecular weight asmeasured by GPC versus polystyrene standards, and Mw/Mn designatesmolecular weight distribution or dispersity. All parts (pbw) are byweight.

Preparation of Additive Polymers

Additive polymers (Polymers 1 to 13) to be added to resist compositionswere prepared by combining suitable monomers, effecting copolymerizationreaction in methyl ethyl ketone solvent, pouring into hexane forcrystallization, repeatedly washing with hexane, isolation, and drying.The polymers were analyzed by ¹H-NMR to determine their composition andby GPC to determine Mw and dispersity Mw/Mn.

Polymer 1

Mw=6,300

Mw/Mn=1.98

Polymer 2

Mw=8,600

Mw/Mn=1.69

Polymer 3

Mw=6,100

Mw/Mn=1.76

Polymer 4

Mw=8,200

Mw/Mn=1.83

Polymer 5

Mw=8,600

Mw/Mn=1.75

Polymer 6

Mw=7,200

Mw/Mn=1.81

Polymer 7

Mw=6,800

Mw/Mn=1.66

Polymer 8

Mw=6,300

Mw/Mn=1.69

Polymer 9

Mw=6,100

Mw/Mn=1.73

Polymer 10

Mw=6,100

Mw/Mn=1.88

Polymer 11

Mw=5,600

Mw/Mn=1.96

Polymer 12

Mw=6,100

Mw/Mn=1.91

Polymer 13

Mw=5,900

Mw/Mn=1.77

Reference Polymer 1

Mw=7,900

Mw/Mn=1.67

Reference Polymer 2

Mw=7,200

Mw/Mn=1.62

Examples and Comparative Examples Preparation of Resist Composition

A positive resist composition in solution form was prepared bydissolving an additive polymer, i.e., resist film surface-modifyingpolymer (Polymers 1 to 13, shown above), a polymer obtained byconventional radical polymerization (Resist Polymers 1 to 5, shownbelow) and components in a solvent in accordance with the formulation ofTable 1 and filtering through a filter with a pore size of 0.2 μm. Notethat the resist preparation is in accord with the method of JP-A2009-263487, paragraph [0192] (U.S. Pat. No. 8,048,610).

EUV lithography patterning test

On a silicon substrate having a diameter of 4 inches, asilicon-containing SOG film of SHB-A940 (Shin-Etsu Chemical Co., Ltd.)was formed to a thickness of 35 nm. The positive resist composition wascoated on the SOG film and prebaked on a hot plate at 110° C. for 60seconds to form a resist film of 35 nm thick. The resist film wasexposed to EUV through a pseudo phase-shift-mask (PSM) in an exposuretool (NA 0.3), baked (PEB) at the temperature shown in Table 2,developed in 0.20N tetrabutylammonium hydroxide (TBAH) aqueous solutionfor 30 seconds, rinsed with deionized water, and spin dried, forming aresist pattern. Sensitivity is the dose at which a 20-nm line-and-spacepattern was formed. Maximum resolution is the minimum size which wasresolved at that dose. The pattern was measured for edge roughness (LWR)under SEM. The results are shown in Table 2.

Resist Polymer 1

Mw=6,700

Mw/Mn=1.58

Resist Polymer 2

Mw=6,900

Mw/Mn=1.68

Resist Polymer 3

Mw=6,200

Mw/Mn=1.81

Resist Polymer 4

Mw=7,200

Mw/Mn=1.51

Resist Polymer 5

Mw=5,200

Mw/Mn=1.61

TABLE 1 Polymer PAG Quencher Additive Surfactant Solvent (pbw) (pbw)(pbw) (pbw) (pbw) (pbw) Resist 1 Resist Polymer 1 — Quencher Polymer 1FC-4430 PGMEA (2,000) (100) (1.123) (2.0) (0.001) PGME (1,000)cyclohexanone (3,000) 2 Resist Polymer 2 — Quencher Polymer 1 FC-4430PGMEA (2,000) (100) (1.123) (2.0) (0.001) PGME (1,000) cyclohexanone(3,000) 3 Resist Polymer 3 — Quencher Polymer 1 FC-4430 PGMEA (2,000)(100) (1.123) (2.0) (0.001) PGME (1,000) cyclohexanone (3,000) 4 ResistPolymer 4 — Quencher Polymer 1 FC-4430 PGMEA (2,000) (100) (1.123) (2.0)(0.001) PGME (1,000) cyclohexanone (3,000) 5 Resist Polymer 5 PAG 1Quencher Polymer 1 FC-4430 PGMEA (4,000) (100) (25) (1.123) (2.0)(0.001) cyclohexanone (2,000) 6 Resist Polymer 1 — Quencher Polymer 2FC-4430 PGMEA (2,000) (100) (1.123) (2.0) (0.001) PGME (1,000)cyclohexanone (3,000) 7 Resist Polymer 1 — Quencher Polymer 3 FC-4430PGMEA (2,000) (100) (1.123) (2.0) (0.001) PGME (1,000) cyclohexanone(3,000) 8 Resist Polymer 1 — Quencher Polymer 4 FC-4430 PGMEA (2,000)(100) (1.123) (2.0) (0.001) PGME (1,000) cyclohexanone (3,000) 9 ResistPolymer 1 — Quencher Polymer 5 FC-4430 PGMEA (2,000) (100) (1.123) (2.0)(0.001) PGME (1,000) cyclohexanone (3,000) 10 Resist Polymer 1 —Quencher Polymer 6 FC-4430 PGMEA (2,000) (100) (1.123) (2.0) (0.001)PGME (1,000) cyclohexanone (3,000) 11 Resist Polymer 1 — QuencherPolymer 7 FC-4430 PGMEA (2,000) (100) (1.123) (2.0) (0.001) PGME (1,000)cyclohexanone (3,000) 12 Resist Polymer 1 — Quencher Polymer 8 FC-4430PGMEA (2,000) (100) (1.123) (2.0) (0.001) PGME (1,000) cyclohexanone(3,000) 13 Resist Polymer 1 — Quencher Polymer 9 FC-4430 PGMEA (2,000)(100) (1.123) (3.0) (0.001) PGME (1,000) cyclohexanone (3,000) 14 ResistPolymer 1 — Quencher Polymer 10 FC-4430 PGMEA (2,000) (100) (1.123)(2.0) (0.001) PGME (1,000) cyclohexanone (3,000) 15 Resist Polymer 1 —Quencher Polymer 11 FC-4430 PGMEA (2,000) (100) (1.123) (2.0) (0.001)PGME (1,000) cyclohexanone (3,000) 16 Resist Polymer 1 — QuencherPolymer 12 FC-4430 PGMEA (2,000) (100) (1.123) (3.0) (0.001) PGME(1,000) cyclohexanone (3,000) 17 Resist Polymer 1 — Quencher Polymer 13FC-4430 PGMEA (2,000) (100) (1.123) (3.0) (0.001) PGME (1,000)cyclohexanone (3,000) Comparative 1 Resist Polymer 1 — Quencher —FC-4430 PGMEA (2,000) Resist (100) (1.123) (0.001) PGME (1,000)cyclohexanone (3,000) 2 Resist Polymer 1 — Quencher Reference FC-4430PGMEA (2,000) (100) (1.123) Polymer 1 (0.001) PGME (1,000) (3.0)cyclohexanone (3,000) 3 Resist Polymer 1 — Quencher Reference FC-4430PGMEA (2,000) (100) (1.123) Polymer 2 (0.001) PGME (1,000) (3.0)cyclohexanone (3,000) PGMEA: propylene glycol monomethyl ether acetatePGME: propylene glycol monomethyl ether FC-4430: fluorochemicalsurfactant by 3M-Sumitomo Co., Ltd.

TABLE 2 PEB Maximum temperature Sensitivity resolution LWR (° C.)(mJ/cm²) (nm) (nm) Resist 1 90 15 17 4.6 2 85 16 18 4.4 3 85 17 17 4.2 485 18 17 4.5 5 85 15 16 4.2 6 90 15 17 4.2 7 90 17 17 4.5 8 90 17 17 4.39 90 17 17 4.6 10 90 16 17 4.7 11 90 18 17 4.7 12 90 19 17 4.7 13 90 1617 4.5 14 90 16 17 4.5 15 90 17 17 4.6 16 90 16 17 4.7 17 90 15 17 4.7Comparative 1 90 15 20 6.0 Resist 2 90 16 19 5.1 3 90 16 19 5.0

Japanese Patent Application No. 2012-277747 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A resist composition comprising a polymer capable of increasingalkali solubility under the action of acid as base resin, and a polymerhaving the general formula (1) as polymeric additive,

wherein R¹ is a single bond or a straight or branched C₁-C₄ alkylene, R²is fluorine, or a straight, branched or cyclic C₁-C₆ alkyl, phenyl oralkyl-substituted phenyl group which contains at least one fluorineatom, R³ and R⁴ are each independently selected from the groupconsisting of hydrogen, hydroxyl, straight, branched or cyclic C₁-C₁₀alkyl, alkoxy, acyloxy, C₂-C₆ alkenyl, C₆-C₁₀ aryl, cyano, nitro, aminoand halogen, X¹ and X² each are phenylene or naphthylene, m is 1 or 2,R⁵ and R⁶ are each independently selected from the group consisting ofhydrogen, halogen, straight or branched C₁-C₄ alkyl, alkoxy, acyloxy,hydroxyl, carboxyl, and alkoxycarbonyl, M is methylene, oxygen atom orsulfur atom, p, q−1, q−2 and q−3 are numbers in the range: 0<p<1.0,0≦(q−1)<1.0, 0≦(q−2)<1.0, 0≦(q−3)<1.0, and 0<(q−1)+(q−2)+(q−3)<1.0. 2.The resist composition of claim 1 which is a chemically amplifiedpositive resist composition.
 3. The resist composition of claim 2wherein the polymer as base resin comprises recurring units having anacid labile group and recurring units having a hydroxyl and/or lactonering adhesive group.
 4. The resist composition of claim 3 wherein thepolymer as base resin has a weight average molecular weight of 1,000 to500,000, and the recurring units having an acid labile group arerecurring units of at least one type selected from recurring units (a1)and (a2) having a carboxyl and/or phenolic hydroxyl group substitutedwith an acid labile group, as represented by the general formula (2):

wherein R¹⁰ and R¹² are each independently hydrogen or methyl, R¹¹ andR¹³ each are an acid labile group, Y¹ is a single bond, a C₁-C₁₂ linkinggroup having at least one of ester (—COO—), lactone ring, phenylene andnaphthylene, a phenylene group or a naphthylene group, Y² is a singlebond, ester (—COO—) group or amide (—CONH—) group, a1 and a2 are numbersin the range: 0≦a1≦0.9, 0≦a2≦0.9, and 0<a1+a2<1.0.
 5. The resistcomposition of claim 4 wherein the polymer comprising recurring units ofat least one type selected from recurring units (a1) and (a2) having acarboxyl and/or phenolic hydroxyl group substituted with an acid labilegroup, represented by the general formula (2), has further copolymerizedtherein recurring units of at least one type selected from sulfoniumsalt units (b1) to (b3), as represented by the general formula (3):

wherein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl, R is a singlebond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH, R⁰³³ isa straight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl (—CO—), ester (—COO—),ether (—O—), or hydroxyl moiety, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷, R⁰²⁹,R⁰³⁰, and R⁰³¹ are each independently a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether moiety,a C₆-C₁₂ aryl group, a C₇-C₂₀ aralkyl group, or a thiophenyl group, A¹is a single bond, -A⁰-C(═O)—O—, -A⁰-O— or -A⁰-O—C(═O)—, A⁰ is astraight, branched or cyclic C₁-C₁₂ alkylene group which may contain acarbonyl, ester or ether moiety, A² is hydrogen, CF₃ or carbonyl, Z¹ isa single bond, methylene, ethylene, phenylene, fluorinated phenylene,—O—R⁰³²—, or —C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is a straight,branched or cyclic C₁-C₆ alkylene, phenylene, fluorinated phenylene,trifluoromethyl-substituted phenylene or alkenylene group, which maycontain a carbonyl, ester, ether or hydroxyl moiety, M⁻ is anon-nucleophilic counter ion, b1, b2 and b3 are numbers in the range:0≦b1≦0.3, 0≦b2≦0.3, 0≦b3≦0.3, and 0<b1+b2+b3≦0.3.
 6. The resistcomposition of claim 1, further comprising at least one of an organicsolvent, basic compound, dissolution regulator, and surfactant.
 7. Theresist composition of claim 1 wherein 0.1 to 50 parts by weight of theadditive polymer is present per 100 parts by weight of the polymer asbase resin.
 8. A pattern forming process comprising the steps ofapplying the resist composition of claim 1 onto a substrate to form acoating, baking, exposing the coating to high-energy radiation, anddeveloping the exposed coating in a developer.
 9. The pattern formingprocess of claim 8 wherein the high-energy radiation is electron beam orsoft x-ray of wavelength 3 to 15 nm.